Reusing PGC & PGD pins

[Demon]

What would you recommend?

(it's a MeLabs USB programmer)




EDIT: 10K seems to work, but I don't want to shoot myself in the foot down the line. I'd hate to invest a lot of time using pins B6 and B7 as input, only to find out I can't do this later on (I'll be using this exact switch configuration - 10K pulled low followed by 10K/0.01uF).

[richard]

are those switches meant to be active high ?

if so then applying somewhat less than vcc to the pic input pins and all those extra components seems a recipe for non success.
for my money i would use the weak pu and have switches active low [don't press buttons when programming is not to much of a constraint]

[Ioannis]

My practice is what Richard noted. Always have either external pull ups or use the port b with the internal pu enabled and active low switch. No other circuit needed and have the Icsp programmer there just fine.

Ioannis

[Demon]

are those switches meant to be active high ?...

They can be whatever they have to be so that it works perfectly. It's my circuit, and I answer to nobody (except those here that know more than me ).

...applying somewhat less than vcc to the pic input pins and all those extra components seems a recipe for non success....

Oddly, it's working as-is.

...i would use the weak pu and have switches active low....

I just checked, 16F18877 has WPUx register for all ports except pins E0, E1 and E2, so that's a plus.

I'm still doing research on all the processes I need, so the switches can easily become active low.

...don't press buttons when programming is not to much of a constraint...

Definitely agree, I never touch the circuit while it's being programmed.

That being said, is 10K a reasonable isolation resistor in this case?

[Ioannis]

Do not risk reliability and toss the resistor.
Use the internal pull-up with low going switch and you will be just fine.

Ioannis

[Demon]

Do not risk reliability and toss the resistor.
Use the internal pull-up with low going switch and you will be just fine.

Ioannis

I'm using the internal pull-ups.

The signal from the encoders reaches the PIC pins with the 10K series and 0.01uF to ground (as per Bourns design), but not if I add that 2nd 10K isolation resistor towards pins B6 and B7.

The original Bourns design has the pull-up/down resistors BEFORE the 10K/0.01uF combo.

(gonna do some experiments)

[richard]

if your re has the possibility that it can be stationary with either A B contact closed [ground] then it will always be possible to stuff up programming and no isolation other than disconnection will work

the isolation objective is
1 don't impose a logic level on the pgm pins that will damage the programmer
2 don't impose a load on the pgm pins that will corrupt the programming signals
3 allow your signal to reach the pins without signal corruption

[Demon]

if your re has the possibility that it can be stationary with either A B contact closed [ground] then it will always be possible to stuff up programming and no isolation other than disconnection will work...

Yup. I've reached the same conclusion.

I have to use a jumper.

It would have been nice to figure out a "built-in" solution, but that's not happening.